Wikipedia (pronounced as [ˌwiˑkiˈpidi.ə] or [ˌwɪki-], also [-ɐ]) is a multi-lingual Web-based free-content encyclopedia. It is written collaboratively by volunteers, allowing articles to be changed by anyone with an internet connection and added by anyone with a Wikipedia member account. The project began on January 15, 2001 as a complement to the expert-written Nupedia, and is now operated by the non-profit Wikimedia Foundation. Wikipedia has more than 2,500,000 articles, including 850,000 in the English-language version. (According to Wikipedia).
I like Wikipedia. There's been a lot of steam about its faintly anarchist approach to information; it's been likened to the old image of monkeys typing randomly until they finally hit on some English classic. Yes, I know it is not nearly so comprehensive nor so accurate as the Encyclopedia Britannica. Wikipedia is often biased, and its entries are more than a little undependable. But it's downright fun to navigate to a page about which you know a little something and add your smidgen of expertise to the mix. It is essentially the same thing as learning things from other people - just because you don't quote your Cousin Midge in your term paper for Introductory Botany, you can still listen to her homespun explanation of pollination.